1. Technical Field
This invention relates to a semi-levered landing gear for an aircraft.
2. Related Technology
A semi-levered landing gear incorporates functionality which allows the length of the landing gear to be increased for take-off and landing, thereby increasing the height of the aircraft above the runway and allowing greater aircraft rotation for a quicker take-off.
Typical landing gear comprises a main hydraulic shock absorber strut having an upper portion adapted to be connected to the underside of the aircraft, and a lower portion telescoping within the upper portion and pivotally connect to a multi-axle bogie. The bogie comprises a bogie beam which extends fore and aft of the aircraft, with axles and wheels mounted on the bogie beam fore and aft of a main pivot, by which the bogie beam is connected to the lower portion of the main strut. An auxiliary actuator is connected between the upper portion of the main strut and the front of the bogie beam to control the angular position of the bogie beam during taxiing, take-off and landing. When taxiing, the bogie beam is held substantially horizontal so that all the wheels contact the runway to support the aircraft, and the auxiliary actuator provides a hydraulic damping function that damps pivoting movements of the bogie as it engages bumps or dips in the runway. The auxiliary actuator also provides a positioning function to position the bogie for take-off and landing. During take-off, as uplift increases, the main strut extends and the auxiliary actuator extends with it to a maximum length. At this maximum length, the front of the bogie beam is restrained in height and the bogie beam tilts downwards at the rear as the main strut continues to extend. The rear wheels therefore maintain contact with the runway while the forward wheels lift off the ground, the length of the landing gear thereby being effectively increased. On landing, a reverse process is performed with the bogie beam tilted downwards towards the rear wheels so that they touch the runway first. As load increases, the auxiliary actuator maintains the height of the front of the bogie position relative to the main strut and the main strut is compressed until all wheels contact the ground.
It is also necessary to provide actuator means to stow landing gear after take-off and to deploy the landing gear for landing. In order that the stowing operation can take place, the bogie beam may need to be positioned in a more horizontal stowing position, and in one example, this is achieved by operation of the main strut.
An object of the invention is to provide an improved semi-levered landing gear.